The present invention relates to a power transmission system and more particularly relates to a drive shaft support for the upper case housing of a marine stem drive unit.
Stem drives for boats are well known and are popular with boat enthusiasts. Typical of these are the units manufactured by Mercury Marine and OMC. The stem drive unit generally consists of the upper gear housing which is adapted to mount on the transom of a boat for pivotal movement about a generally vertical steering axis. The unit also pivots about a generally horizontal pivot axis so the unit may be lifted out of the water. A drive shaft is supported by the upper gear housing and is driven by a drive shaft and U-joint assembly connected to the engine which is normally located within the rear of the boat. A lower gear housing is attached to the lower end of the upper gear housing. A propeller shaft is supported in bearings in the lower gear housing is driven by the vertical drive shaft through a lower gear set.
One problem with stern drive units of the general type described above is that the transmission provided by the manufacturers of such units are limited in their power transfer capacity. It the boat owner wishes to modify or replace the marine engine increasing its performance and horsepower, the transmission may be incapable of transmitting the increased horsepower to the propeller shaft without damage to the transmission. Often the damage occurs to the drive shaft as increased load on the drive shaft will cause it to fail. Such a failure can be very expensive to repair and may result in damage to other engine components.
As a result, boat enthusiasts have been seeking ways to modify the transmission of stern drive units so that such units can handle increased power. Generally approaches have been to increase the bearing capacity and other similar modifications which generally have not proven successful and which are expensive and further require substantial modification to the stern drive unit.
In view of the foregoing, there exists a need for an improved or modified stern drive unit which will accomodate increased engine power and which can be provided both as an original equipment manufactured item or an market unit.
Briefly, the present invention provides a support for the vertical drive shaft of a stern drive unit. The support includes a generally axially extending tubular member having external threads at its lower end. The upper end supports a flange having a bore for a set screw. Additional bores may be provided as an oil transfer location or may also receive a mounting set screw. The tubular member has a taper at its upper end which extends partway into the axial bore. A bearing member, such as a roller or needle bearing, is pressed or otherwise secured within the upper end of the tubular member. The drive shaft support is inserted into a stern drive unit by removing the top cover to provide access to the vertical shaft. The vertical drive shaft is removed and the support is inserted from the top. When inserting the support, the lower threaded end is secured by tightening a retainer, such as a spanner nut, about threads which retainer will engage the housing structure.
The upper end of the support is secured by inserting a fastener, such as a set screw, through one of the bores in the flange with the set screw engaging a component or structure of the upper drive shaft housing. The drive shaft and other components such as the U-joint assembly, top cover and the like can then be attached completing the installation. The drive shaft extends through the support and is coupled to the upper shaft which carries the clutch and gearing. Housing the drive shaft within the drive shaft support will increase the capacity of the drive shaft by a factor of up to three. Preferably the support is fabricated from a high quality stainless steel or chrome moly steel such as 4140 or 4130.